Demand has increased in recent years for non-aqueous electrolyte secondary batteries as so-called portable power sources for personal computers, hand-held devices, and the like, or as power sources for driving vehicles. In particular, lightweight lithium ion secondary batteries able to achieve high energy densities can be used as high output power sources for driving vehicles such as electric vehicles and hybrid vehicles.
In non-aqueous electrolyte solutions used in such secondary batteries, the types of solvent and supporting salt (electrolyte) are selected and used from perspectives such as improving the performance and durability of a battery. For example, Japanese Translation of PCT Application No. 2015-528640 (WO2014/081254) discloses a non-aqueous electrolyte solution for a lithium ion secondary battery, which is provided in order to improve the ionic conductivity of a non-aqueous electrolyte solution in low temperature regions by suppressing an increase in viscosity of the electrolyte solution, and which is characterized in that 10 to 90 wt. % of the overall solvent is an ester-based solvent and 10 to 90 wt. % of the overall solvent is a carbonate-based solvent.